Developers of athletic shoes are confronted with the problem of storing energy in the sole of the shoe and releasing the energy in a manner which improves the efficiency of the locomotor system to propel the body forward.
Many examples of running shoes exist; however, very few, if any, have been embraced by runners and foot specialists. Studies of the dynamics of the human foot reveal that the longitudinal arch of a human foot, with its numerous joints and ligaments, is capable of returning 70% of the energy put into it and that it is far more efficient than the soles of the best existing running shoes. See Discovery, October 1989 (pp. 77-83). If runners could run with bare feet, many would prefer to do so. However, impact forces are too great and the foot needs protection, especially on hard surfaces.
Athletic shoes have been proposed which have not been entirely satisfactory in that either the stored energy of heel-strike is not transmitted to the runner in the most effective manner to maximize running efficiency or the energy which enhances running efficiency is stored during the push-off period of the running cycle, thereby, impact energy losses are not used. These problems are overcome by the present invention. The inventors hereof have discovered that for heel-toe running, energy should be stored in the sole of the shoe at heel-strike and then, in turn, this stored energy should be released at a critical time and in a particular manner to enhance toe-off propulsion.
While purporting to provide for maximum performance, the latest technology in running shoes fails to achieve the ultimate design which permits maximum storage and return of energy for a variety of running modes ranging from heel-toe running (long-distance) to flat-footed running or toe running (sprinting).
U.S. Pat. No. 4,941,273 (Gross) discloses an athletic shoe having a sole arrangement which contains an elastic band extending through a longitudinal passageway in the mid-sole. The purpose of this device is to create an artificial tendon by facilitating the storage and release of strain energy created during the running cycle. However, because of the position of the elastic band relative to the sole plate, the energy stored at heel strike is not transmitted to the toe to enhance toe-off propulsion.
On the other hand, U.S. Pat. No. 4,492,046 (Kosova) describes a sole of a running shoe having a wire spring. The wire spring serves to bias the anterior portion of the sole from the heel (back of the shoe) forward to the arch region, separating the anterior of the sole into upper and lower portions. The objective of this device is to enhance the runner's performance by reducing impact at heel-strike and launching the runner forward into a comfortable stride. Unfortunately, this device in practice provides energy return immediately at heel-lift, precluding storage of energy which could otherwise be used to propel the runner forward as claimed in the disclosed invention.
The latest commercial running shoes fail to completely address the desired attributes of a properly designed running shoe. For example, several attempts at returning energy only provide a heel-lift assist, permitting little forward propulsion. Others, although claiming to facilitate propulsion at toe-off, are incapable of storing the kinetic (muscle-generated) and potential energies of the runner at heel-strike, allowing a fraction of these energies to be lost to heat and to internal joint resistance (internal damping).
Similar challenges have confronted developers of lower-extremity prosthetic limbs. While it has effected substantial improvements, prosthetic research has so far focused almost exclusively on simulation or duplication of a natural foot in an attempt to provide the amputee with a normal gait and a greater degree of comfort. See U.S. Pat. No. 4,652,266 (Truesdell). A recent improvement emerging from prosthetic research is the College Park Foot design disclosed in U.S. Pat. No. 4,892,554 (Robinson). This design describes a prosthetic foot having an ankle member, a heel member and an elongated metatarsal-toe member coupled to each other for relative pivotal movements. The toe member is partially bifurcated at its forward end to provide independently flexible toe sections at the inner and outer sides of the foot. This design thus represents a three-point balance system achieving a stable support matching that of a natural foot.
One notable exception is the device disclosed in U.S. Pat. No. 4,822,363 (Phillips). This patent describes a composite prosthetic foot having a leg portion, a foot portion and a heel portion all rigidly joined and all three provided with substantial elasticity to allow return of energy absorbed and permit the amputee to engage in sports such as running and playing tennis. Understandably, this design has met with general approval from amputees who are sport enthusiasts, and at the same time enjoyed commercial success.
Like its running shoe counterpart, the above disclosed invention does not contain a mechanism whereby energy absorbed at heel-strike can be stored and later released at the critical moment to create forward propulsion. In addition, the device does not have significant means for storing energy upon impact for the flat-footed runner, i.e., no real longitudinal arch.
The present invention represents a significant improvement over the prior art. Included in the design of the present invention is a collapsible, longitudinal arch formed by coupled springs which operates to delay the release of absorbed energy until toe-lift, thereby propelling the runner forward into a comfortable stride. The purpose of the present invention is to minimize energy losses during the impact phase and to use these energies to improve the runner's overall efficiency. The design can be incorporated into either a shoe for use with a natural foot or a foot prosthesis specially fabricated for amputees wishing to participate in athletic activities. Moreover, the present invention maximizes the runner's performance in all running modes including heel-toe running, sprinting and running flat-footed.